Previous research used the context-free Big Five model of personality traits to predict social media behaviors. The perspective implicit in this research assumes that expression of the Big Five is free of situational context. This thesis challenges this assumption to address whether people express the same Big Five on social media as offline. In two studies, this thesis addressed three issues: (1) whether there are self-reported differences in the Big Five between social media/online and offline contexts, (2) whether a five-factor structure replicates in the offline and social media context reports, and (3) whether the predictive validity of the Big Five is the same between offline and social media contexts. College students (total N = 2102) reported their offline and social media Big Five. Main findings reveal that, first, all of the Big Five have lower expressions in social media/online than offline, except for those in the lowest quartile of offline trait expressions; possible explanations include regression towards the mean or the environmental impact of social media. Second, a similar factor structure appeared with openness, extraversion, and neuroticism items being the most robust between offline and social media contexts. However, some conscientiousness and agreeableness items did not apply across offline and social media contexts. Third, the Big Five had different predictive patterns of social media behaviors depending on the context. These findings inform that future research may better serve to specify the context of Big Five expression to understand social media behavior.